Dynamic weighing modules intended to be used with franking machines are well known. French Patent Application No. 2 388 352 illustrates a particular example thereof. These devices are formed by a weighing deck and drive belts for automatically conveying the mail items from one side of this deck to the other. The weighing module may be used alone but it is usually interposed in a mail handling assembly between the exit of the feed module from which the closed envelopes having to be franked are ejected, and the entrance of the franking module.
Accompanying FIG. 4 illustrates the essential elements of such a weighing module. The weighing cell 10 used in this type of module is a conventional load sensor comprising flexible elements, strain gauges and the associated wirings and it is therefore unnecessary to describe it. Models PV2GC3 of the firm HBM or 1042 of the firm TEDEA are classic examples thereof. This cell is mounted between two platforms, a fixed lower platform 12 and a mobile upper platform 14, and is fixed thereto, via two shims 16, 18, by screws 20, 22 which traverse them. Two assemblies 24, 26 of vertical feet arranged at the four comers of these two platforms extend towards each other (the feet fast with the lower platform upwardly, and the feet fast with the upper platform downwardly) in order to define therebetween a free space G corresponding to the maximum load admissible by the cell.
During transport of a weighing module, it is usual to immobilize the weighing sensor by maintaining the two platforms by a relatively complex securing system while arranging shims between the vertical feet to remain in an acceptable zone of constraint of the sensor. Now, if the module remains a long time in this position before it is delivered to the client, the pre-stress exerted on the sensor most often necessitates a recalibration of the weighing cell after the platforms have been released. In addition, the securing of the platforms is generally effected vertically in the sense of weighing, this involving at least lifting the cover of the module, possibly dismantling certain parts, sometimes even turning the machine over to unscrew the screws ensuring this securing.
It is an object of the present invention to propose considerably simplifying this system of immobilizing the weighing cell during transport thereof with the aid of a simple, economic means without exerting pre-stress on the sensor, this allowing the weighing module to be instantaneously restarted. Another object of the invention is to ensure such immobilization with a minimum of operations in the factory and to allow the sensor to be released by the user without intervention inside the module.